1. Field of the Invention
This invention relates to antistatic thermoplastic molding masses based on copolymers of styrene and/or .alpha.-methylstyrene and acrylonitrile, such as styrene-acrylonitrile-copolymers (SAN polymers), styrene-acrylonitrile copolymers modified with butadiene rubber (ABS polymers), styrene-acrylonitrile copolymers modified with acrylate elastomers (ASA polymers), and styrene-acrylonitrile copolymers modified with EPDM rubber (AES polymers), optionally modified by rubberlike polymers, and containing as an antistatic agent a graft polyol which is a polyhydroxy-polyalkylene polyether modified with a styrene-acrylonitrile copolymer.
2. Description of the Prior Art
The addition of antistatic agents to thermoplastic molding masses based on vinyl aromatic-acrylonitrile-copolymers is part of the current state of the art. Suitable known antistatic agents include amines, amides, salts of quaternary ammonium bases, sulfonic acids, alkyl, aryl, alkylaryl sulfonates, phosphoric acids, alkyl, aryl or alkylaryl phosphates, polyoxyethylene polyoxypropylene copolymers, alkyl or arylethers and esters thereof, including inorganic as well as organic acid residues as acid components. The agents are added to suppress the dust accumulation on finished parts. Such antistatic agents used in thermoplastic molding masses are described, for instance, in German Pat. Nos. 1,244,398 and 1,258,083.
All of these molding masses have negative factors. The use of low molecular weight antistatic agents frequently results in the formation of a coating on the surface of molds and finished parts and reduced dimensional stability when exposed to heat. If oligomeric or polymeric antistatic substances are used, reduced impact strength and unfavorable processing properties occur.
A purpose of this invention was to find antistatic agents which are particularly compatible with vinyl aromatic-acrylonitrile copolymers and do not form a coating of the surfaces of molds and parts, do not reduce the thermal dimensional stability and the impact resistance of the finished parts, do not result in unfavorable processing properties and do not result in a clouding or discoloration of the finished parts and which at the same time have a very good antistatic behavior and must be used in small quantities.
It has been found that this problem is solved by the addition of a graft polyol, which is a polyhydroxy-polyalkylene polyether modified with styrene-acrylonitrile copolymers, to the molding mass.